MAN B&W 7.01
Page 3 of 3
MAN Diesel
MAN B&W K98MC, K98MCC, S90MC-C, K90MC-C,
S80MC, S80MC-C, K80MC-C, S70MC, S/L70MC-C,
S60MC, S/L60MC-C, S50MC, S50MC-C, S46MC-C
198 67 78-0.1
When the engine is stopped, the circulating
pump will continue to circulate heated heavy fuel
through the fuel oil system on the engine, thereby
keeping the fuel pumps heated and the fuel valves
deaerated. This automatic circulation of preheated
fuel during engine standstill is the background for
our recommendation:
Constant operation on heavy fuel
In addition, if this recommendation was not fol-
lowed, there would be a latent risk of diesel oil
and heavy fuels of marginal quality forming in-
compatible blends during fuel change over or
when operating in areas with restrictions on sul-
pher content in fuel oil due to exhaust gas emis-
sion control.
In special circumstances a changeover to diesel
oil may become necessary – and this can be per-
formed at any time, even when the engine is not
running. Such a changeover may become neces-
sary if, for instance, the vessel is expected to be
inactive for a prolonged period with cold engine
e.g. due to:
• docking
• stop for more than five days
• major repairs of the fuel system, etc.
Heating of fuel drain pipe
Owing to the relatively high viscosity of the heavy
fuel oil, it is recommended that the drain pipe and
the fuel oil drain tank are heated to min. 50 °C, but
max. 100 °C.
The drain pipe between engine and tank can
be heated by the jacket water, as shown in Fig.
7.01.01 ‘Fuel pipe heating’ as flange ‘BD’.
Fuel flow velocity and viscosity
For external pipe connections, we prescribe the
following maximum flow velocities:
Marine diesel oil .......................................... 1.0 m/s
Heavy fuel oil .............................................. 0.6 m/s
The fuel viscosity is influenced by factors such
as emulsification of water into the fuel for reduc-
ing the NO
x
emission. This is further described in
Section 7.06.
An emulsification arrangement for the main en-
gine is described in our publication:
Exhaust Gas Emission Control Today and
Tomorrow
Further information about fuel oil specifications is
available in our publication:
Guidelines for Fuels and Lubes Purchasing
The publications are available at:
www.mandiesel.com under
‘Quicklinks’ → ‘Technical Papers’.
Fuel considerations
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